GB1563208A

GB1563208A - Developer for electrostatic photography

Info

Publication number: GB1563208A
Application number: GB44254/76A
Authority: GB
Original assignee: Mita Industrial Co Ltd
Current assignee: Kyocera Mita Industrial Co Ltd
Priority date: 1975-10-27
Filing date: 1976-10-25
Publication date: 1980-03-19
Also published as: JPS57494B2; IT1067694B; US4264698A; DE2648258C2; NL7611893A; FR2330039A1; DE2648258A1; JPS5252639A; NL183963C; FR2330039B1

Description

( 21) Application No 44254/76

( 31) Convention Application Is ( 32) Filed 27 Oct 1975 in ( 33) Japan (JP) ( 22) Filed 25 Oct 1976 4 o 50/128313 ( 44) Complete Specification published 19 March 1980 ( 51) INT CL 3 G 03 G 9/08 ( 52) Index at acceptance G 2 C 1102 1103 1104 1105 1106 1107 1108 1109 1112 1113 1114 1115 1116 1118 1119 1120 1121 1125 1126 1129 1130 1131 1132 1133 1134 1165 1171 1172 1173 C 17 Q 2 ( 54) DEVELOPER FOR ELECTROSTATIC PHOTOGRAPHY ( 71) We, MITA INDUSTRIAL COMPANY LIMITED a Japanese Body Corporate of No 5, Miyabayashi-cho.

Higashi-ku, Osaka, Japan, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement:-

This invention relates to a developer for electrostatic photography and a process for the preparation of the developer.

A so-called magnetic brush method is broadly used as a method for developing electrostatic latent images formed by electrostatic photography In early magnetic brush developing methods, particles of a developer (toner) comprising a pigment and a resin for imparting the fixing property and desirable electrical characteristics to the pigment are mixed with a magnetic carrier such as iron powder, and the mixture is closely contacted with the surface of a support having a magnetic brush and carrying an electrostatic latent image to thereby render visible the latent image with the developer particles.

According to this method using a mixture of the toner and magnetic carrier, however, only the developer particles in the mixture are consumed and the ratio of the developer:magnetic carrier is changed in the mixture Accordingly, the supply of toner in the mixture must often be replenished to keep a prescribed balance between the developer and magnetic carrier This is a very troublesome operation.

As toners capable of performing development without the aid of a particular carrier, there are known so-called magnetic toners, such as those disclosed in U K.

Specifications Nos 1,282,017 and 1,406,983.

These magnetic toners are generally prepared by dispersing a powder of a magnetic material such as triiron tetroxide, if necessary with additives such as a pigment, into a medium of a binder resin and cooling and pulverising the resulting mass to form particles In order to render the surfaces of the particles electrically conductive, an electrically conductive substance such as carbon black is embedded in or deposited on the surface of the particles.

These magnetic toners have an advantage that clear toner images with a much reduced edge effect can be produced according to the magnetic brush development method without using a magnetic carrier However, production of these magnetic toners can present difficulties and may involve a complicated series of steps For example, in accordance with Specification No.

1,282,017, a powder of a magnetic material, optionally with a pigment such as carbon black, is uniformly dispersed in a melt of a binder resin medium, the mixture is allowed to cool and the cooled mass is pulverised to form a particulate powder This powder is then aspirated into a moving gas stream to create an aerosol, which is directed at about OF through a stream of hot air into a cooling chamber, where the powder is allowed to cool and settle under gravity It is then dry blended with a conductive powder and then heated to at least soften and desirably melt the binder resin for sufficient time to allow the conductive powder to become essentially completely embedded in the particles.

Further, when magnetic toners containing particles of a large particle size are employed, the resolving power is low in developed copies, and when magnetic toners containing particles of an extremely small particle size are employed, so-called fog is caused on development Accordingly, in magnetic toners prepared according to the conventional process, the particle size should inevitably be adjusted for example by sieving, resulting in reduction of Yields of toners.

Moreover, various problems can be caused by poor flowability of known toner particles in the developing operation For 0 o or 4 PATENT SPECIFICATION (Ii) 1 563 208 1,563208 example, the known magnetic toners may not have a flowability sufficient to distribute the toner particles uniformly on a developing roller (sleeve) Masses or agglomerates of the toner particles are often formed on the surface of the sleeve and they often fall on a copying sheet to contaminate the background of the obtained copy.

Moreover, because of non-uniform adhesion of the toner particles on the surface of the sleeve, the resulting image is often blurred.

As means for improving the flowability in particles of magnetic toners, there is known a method in which finely divided silica is incorporated as a lubricant into particles of magnetic toners However, since finely divided silica adhering to the peripheries of the toner particles has a relatively high electric resistance, the electric resistance of the developer as a whole is increased and therefore such undesirable phenomena as bleeding of contours of the resulting image can be caused to occur.

According to this invention, there is provided a flowable developer having a volume resistivity not higher than 1012 (Q-cm, suitable for use in electrostatic photography, said developer consisting essentially of a dry blend of (A) substantially spherical magnetic particles comprising a binder medium with from 20 % to 80 % by weight, based on the weight of particles (A), of particles of a magnetic material distributed therein, said particles (A) having a rough surface formed by spray-drying a dispersion of said magnetic particles distributed in a solution of said binder medium in an organic solvent and having an average particle size of from I to 100 microns, and (B) particles of a material having a volume resistivity not higher than l O '2 Q-cm, said particles (B) having an average particle size not larger than 1/10 of the average particle size of the particles (A) and being distributed predominantly on the surface of the particles (A) the particles (A) and (B) being present in a weight ratio of (A):(B) of from 10000:1 to 50:1.

The developer particles of this invention have a good flowability, making them suitable for the developing operation, and a low electric resistance necessary for providing sharp images The developer of this invention has a flowability sufficient to distribute the developer particles uniformly on a developing sleeve, and hence, occurrence of such undesirable phenomena as contamination of the background, caused by agglomerates of developer particles falling onto the copying sheet, and the formation of blurred images, caused by uneven adhesion of the developer particles, can be effectively prevented.

Further, the developer of this invention has volume resistivity not higher than I x 1012 -cm, especially not higher than l x 10 '0 Q-cm, irrespective of the humidity in the atmosphere Because of this electrical characteristic, when the developer of this invention is used, a visible image having no bleeding in contours and a much reduced edge effect can be obtained.

The particles (A) of the developers of the present invention may be prepared by dissolving the binder medium in an organic solvent so that the binder medium concentration in said solvent is not higher than 30 ", by weight, dispersing a fine powder of a magnetic material in the resulting solution, spray-drying the resulting slurry and, if appropriate, sieving the resulting particles.

In known magnetic toners prepared by merely dryblending a magnetic material with carbon black, at the step of developing electrostatic latent images, carbon particles separated from the magnetic toner will adhere to the background to reduce the clearness of formed copies For this reason, in conventional magnetic toners the carbon black particles are embedded in the surface portion of the magnetic toner In contrast, in the present invention when spherical particles (A) are merely dry-blended with particles (B) of carbon black and the dry blend is applied to a photosensitive layer having an electrostatic latent image formed thereon, as is apparent from all the Examples given hereinafter, no contamination is caused on the background, the flowability of the developer can be greatly improved and bleeding of the toner image may be much reduced It is believed that attainment of this unexpected effect is due to the fact that the magnetic particles (A) in the developer of this invention have coarse surface due to the presence of surface projections and indentations caused by the spray-drying operation This rough surface is thought to be the reason why the smaller particles (B) such as carbon black, to adhere to the surface of the spherical particles (A), for example during the development step The fine particles (B) may be considered as controlling the flowability and electric resistance of the developer of the invention.

The developer for electrostatic photography according to this invention can easily be fixed on a copying paper by customary heat-fixing means, and it has the characteristic property that it can readily be fixed on a copying paper under a relatively low pressure More specifically, since the magnetic particles (A) in the developer of this invention have crater-like rough surfaces (confirmed by a layer oil absorption and from photographs taken through a microscope) formed by coagulating a magnetic material-binder medium dispersion in a drying atmosphere.

the developer of this invention has a sufficient anchoring effect to a photoconductive layer or coating of a copying paper even under a relatively low pressure Because of this characteristic property, developer particles may be readily embedded in the photosensitive layer or coating of a copying paper under application of pressure at the fixing step and hence, a strongly fixed image can be readily formed on the copying paper.

The substantially spherical magnetic particles (A) of the developer of this invention can be prepared by spraying a dispersion of a fine powder of a magnetic material and a binder medium in an easilyvolatile solvent in a drying atmosphere to thereby solidify (coagulate) the dispersion in the particulate form.

The fine powder of the magnetic material has preferably a particle size smaller than 1000 mp, especially preferably a particle size smaller than 500 my.

As inorganic magnetic materials that can be used in this field, there can be mentioned, for example, triiron tetroxide (Fe 304), diiron trioxide (y-Fe 2 03), zinc iron oxide (Zn Fe 2 04), ytterium iron oxide (Y 3 Fe 5 O,2), cadmium iron oxide (Cd Fe 2 04), copper iron oxide (Cu Fe 2 04), lead iron oxide (Pb Fe,2 O,1), nickel iron oxide (Ni Fe 204), neodium iron oxide (Nd Fe 203), barium iron oxide (Ba Fe,2 O,), magnesium iron oxide (Mg Fe 204), manganese iron oxide (Mn Fe 204), lanthanum iron oxide (La Fe O 3), iron powder (Fe), cobalt powder (Co) and nickel powder (Ni) In this invention, at least one member selected from the foregoing magnetic materials may be used Use of triiron tetroxide as the magnetic material is especially preferred.

Any of natural, semi-synthetic and synthetic resins and rubbers or a wax having a suitable adhesiveness under application of heat or pressure can be used as the binder medium in which the magnetic material is distributed These resins may be thermoplastic resins, or uncured thermosetting resins or precondensates thereof As valuable natural resins, there can be mentioned, for example, balsam, rosin, shellac, and copal These natural resins may be modified with one or more of vinyl resins, acrylic resins, alkyd resins, phenolic resins, epoxy resins and oleoresins (oil resins) such as mentioned below As the synthetic resin that can be used in the present invention, there can be mentioned, for example, vinyl resins such as vinyl chloride resins, vinylidene chloride resins, vinyl acetate resins and vinyl acetal resins, e.g polyvinyl acetal: acrylic resins such as polyacrylic acid esters, polymethacrylic 65 acid esters, acrylic acid copolymers and methacrylic acid copolymers; olefin resins such as polyethylene, polypropylene, polystyrene and styrene copolymers; polyamide resins such as nylon-12, nylon-6 and polymeric 70 fatty acid-modified polyamides; polyesters such as polyethylene terephthalate/isophthalate _ and polytetramethylene terephthalate/isophthalate: alkyd resins such as phthalic acid resins and maleic acid 75 resins; phenolformaldehyde resins; ketone resins; coumarone-indene resins: amino resins such as urea-formaldehyde resins and melamine-formaldehyde resins; and epoxy resins These synthetic resins may be used in 80 the form of mixtures, for example, a mixture of a phenolic resin and an epoxy resin or a mixture of an amino resin and an epoxy resin.

As the natural and synthetic rubbers that 85 can be used in the present invention, there can be mentioned, for example, natural rubber, chlorinated rubber, cyclized rubber, polyisobutylene, ethylene-propylene rubber (EPR), ethylene-propylene-diene monomer 90 rubber (EPDM), polybutadiene, butyl rubber, styrene-butadiene rubber (SBR) and acrylonitrile-butadiene rubber.

In this invention, it is important that the finely divided magnetic material should be 95 incorporated at such a ratio that the finely divided magnetic material is present in an amount of 20 to 80 ,% by weight, especially to 60 % by weight, based on the spherical particles (A) In the case where the amount 100 of the finely divided magnetic material is smaller than 20 %' by weight, it is difficult for the spherical particles (A) to be sufficiently magnetically attractable When the amount of the finely divided magnetic material 105 exceeds 80 Y by weight, the form-retaining property is often degraded in the resulting spherical particles (A).

In order to improve the color or hue of the spherical particles (A) and to extend the 110 spherical particles (A), various dyes, pigments and extender pigments may be incorporated in the particles (A) Suitable examples of these dyes, pigments and extender pigments are as follows: 115 Black Pigments:

Carbon black, acetylene black, lamp black and Aniline Black Yellow Pigments:

Chrome yellow, zinc yellow, cadmium 120 yellow, yellow iron oxide, Mineral Fast Yellow, nickel titanium yellow, Nablus Yellow, Naphthol Yellow S, Hansa Yellow G, Hansa Yellow IOG, Benzidine Yellow G, Benzidine Yellow GR, Quinoline Yellow 125 Lake, Permanent Yellow NCG and Tartrazine Lake I 1,563,208 1 563,208 Orange Pigments:

Chrome orange molybdenum orange, Permanent Orange GTR, Pyrazolone Orange, Balkan Orange, Indanthrene Brilliant Orange RK, Benzidine Orange G and Indanthrene Brilliant Orange GK Red Pigments:

Red iron oxide cadmium red, red lead, cadmium mercury sulfide, Permanent Red 4 R Lithol Red, Pyrazolone Red, Watchung Red Calcium salt, Lake Red D, Brilliant Carmine 6 B Eosine Lake, Rhodamine Lake B Alizarine Lake and Brilliant Carmine 3 B Violet Pigments:

Manganese violet, Fast Violet B and Methyl Violet Lake Blue Pigments:

Ultramarine, cobalt blue, Alkali Blue Lake, Victoria Blue Lake, Phthalocyanine Blue, metal-free Phthalocyanine Blue, partially chlorinated Phthalocyanine Blue, Fast Sky Blue and Induthrene Blue BC Green Pigments:

Chrome Green, chromium oxide, Pigment Green B, Malachite Green Lake and Fanal Yellow Green G White Pigments:

Zinc flower, titanium oxide, antimony white and zinc sulfide Extender Pigments:

Baryta powder, barium carbonate, clay, silica, white carbon (a white reinforcing filler for rubber which is composed of fine silica powder), talc and alumina white Dyes (basic, acidic, disperse and direct dyes):

Nigrosine Methylene Blue, Rose Bengale, Quinoline Yellow and Ultramarine Blue.

It is preferred that these pigments and extender pigments have a particle size equal to or smaller than the size of the finely divided magnetic material They may be used in an amount of less than 50 ?-,, by weight, especially less than 10 ' by weight, based on the particles (A).

In this invention, it is preferred that the substantially spherical magnetic particles (A) comprise 40 to 60 ,, by weight of a finely divided magnetic material, 30 to 59 %/,, by weight of a binder medium such as a resin, a rubber or a wax and I to 10 ,, by weight of carbon black.

As the easily-volatile solvent for dispersing the finely divided magnetic material and binder medium, there can be used any of solvents capable of dissolving therein the binder medium and volatilizing in a drying atmosphere For example, there can be mentioned lower alcohols such as methanol, ethanol, propanol and various -'Cellosolves" ("Cellosolve" is a Registered Trade Mark), ketones such as acetone and methylethyl ketone ethers such as tetrahydrofuran and dioxane, amides such as N,N-dimethylformamide and NNdimethylacetamide, amines such as morpholine and pyrrolidone sulfoxides such as dimethylsulfoxide, aromatic hydrocarbon solvents such as benzene, toluene and xylene, halogenated hydrocarbon solvents such as chloroform.

carbon tetrachloride, trichlene, perchlene and freon, esters such as ethyl acetate and amyl acetate, and other organic solvents.

These solvents may be used singly or in the form of a mixture of two or more of them.

Suitable kinds of solvents are chosen depending on the kinds of the binder media used.

Fine surface projections and indentations can be effectively formed on the spherical particles, by causing prompt evaporation of the organic solvent at the spray-drying granulation step When a resin such as an epoxy resin is used as the binder medium, it is preferred to use an easily volatile organic solvent having a boiling point lower than 'C and a vapor pressure higher than 100 mm Hg at 200 C, such as acetone When a wax is used as a binder medium, in view of the dissolving power it is necessary to use an aromatic organic solvent such as hot toluene In this case, it is preferred to heat the spraying liquid used in the spray-drying step in advance and to increase the temperature of the drying atmosphere to a considerably high level, for example 1500 C, to cause prompt evaporation of the solvent.

The solid concentration in the dispersion is chosen so that the dispersion can be sprayed and can easily be solidified (coagulated) in spherical particles in a drying atmosphere In general, the solid concentration of the dispersion is in the range of from 20 to 80 %, by weight, preferably in the range of 40 to 60 %,, by weight It is especially preferred that the resin concentration be in the range of 5 to %", by weight, especially 8 to 20 ,, by weight.

This spraying dispersion can readily be prepared by mixing a solution or dispersion of the binder medium in a solvent such as mentioned above with the above-mentioned amount of a powder of a magnetic material by known dispersing means such as ultrasonic vibration, homogenizing or ball milling The so prepared dispersion is sprayed in a drying atmosphere to effect granulation.

In this invention, as the drying 1,563 208 atmosphere there are employed various gases such as air, nitrogen, carbon dioxide gas and combustion gas (for example the waste gas from boilers), heated at 5 to 2000 C, especially gases heated at a temperature higher than the boiling point of the solvent used A dispersion of the fine powder of the magnetic material and the hinder medium is sprayed into such drying atmosphere At this spraying step, the high temperature gas acts as a dispersion medium and the sprayed dispersion is present in the gas in the form of spherical particles In this state, the solvent is evaporated off into the high temperature gas Evaporation of the solvent first occurs in the surface portions of the sprayed spherical particles and as the solvent in the interiors of the particles volatilizes, the volumes of the particles decrease and pores are formed on and in the particles by evaporation of the solvent As a result fine surface projections and indentations (convexities and concavities) are formed on the surfaces of the particles In order to form such fine surface projections and indentations effectively, it is important that the binder medium concentration in the dispersion to be sprayed should be not higher than 30 ,, by weight.

The particle size of the so formed spherical particles depends on such factors as the solid concentration and viscosity of the dispersion to be sprayed, the speed of spraying the dispersion and the temperatures and velocity of the drying atmosphere In this invention, these conditions are set so that the resulting spherical particles have an average particle size of from I to 100 microns, preferably from 2 to 50 microns, and preferably a particle size distribution such that from 0 to ',, of particles (A) have a particle size larger than 44,u from 0 to 10 ,, of particles (A) have a particle size smaller than 2 At.

Various known means may be adopted for spraying the dispersion of a fine powder of a magnetic material and a binder medium.

For example, there can be used a one-fluid or two-fluid nozzle, a centrifugal spray nozzle comprising a rotary member having a number of holes formed on the circumferential wall thereof, a rotary disc and the like The so obtained particles (A) are, if desired, dried under reduced or atmospheric pressure under such conditions such that substantial fusion of the binder medium is not caused, whereby the remaining solvent can be removed from the particles Then, the particles (A) are used for production of the developer of this invention.

Since the particles (A) that are used in this invention have rough surfaces, they have an oil absorption of from 25 to 40.

especially from 28 to 35.

The oil absorption referred to in this specification is determined according to JIS

K-8101 in the following manner:

A sample ( 10 g) is charged in a beaker.

and purified linseed oil is gradually added dropwise to the sample Every time a prescribed amount of linseed oil is added.

the mixture is kneaded by a glass rod The addition and kneading operations are continued until the mixture can be drawn upwardly in stiff rodlike peaks when the kneading rod is lifted up from the mixture and linseed oil is in the state oozing out on the surface of the mixture The oil absorption is calculated according to the following equation:

Ax 100 Oil Absorption= B wherein A stands for the amount (g) of linseed oil added dropwise to the sample and B denotes the amount (g) of the sample.

According to this invention, the so prepared substantially spherical fixing magneto-sensitive particles (A) are dryblended with the particles (B) Particles (B) preferably having a particle size of less than 4 microns, especially smaller than 0 1 micron, and a volume resistivity not higher than 10 '2 Q-cm, preferably not higher than l 010 'Q-cm As indicated previously, the presence of particles (B) is believed to control the flowability and electrical resistance of the developer of the invention.

There can be employed carbon black, inorganic fine particles which are nonconductive in themselves but which are treated such that the resulting particles are electrically conductive, and various metal powders as the particles (B).

As the carbon black having a particle size not larger than 4,u and a volume resistivity not higher than 1012 _-cm, there can be used, for example, furnace black for rubbers, channel black for cells or rubbers and channel black for pigments Especially preferred Carbon black includes conductive carbon black Corox-L manufactured by Degussa Co and Vulcan XC-72 R manufactured by Cabot, Inc.

Further, particles of metal oxides such as diiron trioxide, triiron tetroxide and dinickel trioxide and ultrafine particles of metals such as iron, cobalt, copper, silver, gold, aluminum and tin can also be used as the particles (B) Moreover, particles of inorganic substances such as silicon dioxide, activated clay, acid clay, kaolin, alumina powder and zeolite, which are nonelectrolytically plated with such metals as 6 1563208 gold silver and copper, may be used as the fine particles (B) in this invention.

As the particles (B), there may alternatively be used particles of an inorganic substance which are nonconductive in themselves but which are treated in such a way that the resulting particles are electrically conductive The inorganic non-conductive particles, or -carrier particles" preferably have a good flowabilitv and a capacity of absorbing or adsorbing therein a surface active agent a dye and a conductive resin The dye acts as a pigment It is the presence of the surface active agent, which has a high moistureretaining ability and is used broadly as an antistatic agent, and/or conductive resin absorbed by or adsorbed on the carrier particles which gives the resulting particles the necessary electrical properties For example silicon dioxide, activated clay, acid clay, kaolin, alumina powder and zeolite are preferably employed It is essential that the average particle size of such inorganic carrier particles be smaller than 1/10 of the average particle size of the particles (A), especially smaller than 4 u, especially preferably smaller than 0 1 Mu.

As suitable examples of silicon dioxide carrier particles, there can be mentioned "Aerosil" 200, "Aerosil" R 972, Silica D 17 and Sipernat 17 manufactured by Nippon Aerosil K K ("Aerosil" is a Registered Trade Mark) Fine particles of acid clay, kaolin and zeolite can also be preferably used as the inorganic "carrier particles".

A solvent suitable for absorbing or adsorbing a surface active agent, a conductive resin or a dye on such inorganic carrier particles is one capable of dissolving the appropriate surface active agent, dye and resin but incapable of dissolving the carrier particles Moreover, the solvent is desired to have such a property that it volatilizes by drying and is not substantially left in the carrier particles after drying.

As such solvent, there can be mentioned, for example, lower alcohols such as methanol, ethanol and propanol, ketones such as acetone, ethers such as tetrahydrofuran and dioxane, amines such as morpholine and pyrrolidone, sulfoxides such as dimethylsulfoxides, aromatic hydrocarbons such as benzene, toluene and xylene, halogenated hydrocarbons such as chloroform, carbon tetrachloride, trichlene, perchlene and "Freon", esters such as ethyl acetate and amyl acetate, and water ("Freon" is a Registered Trade Mark).

A dye dissolved in such solvent is absorbed or adsorbed on the inorganic carrier particles The kind of the dye is not particularly critical and in practice most dyes can be used.

For example, direct dyes, basic dyes, acid dyes, mordant dyes reactive dyes, acid mordant dyes, fluorescent dyes and oilsoluble dyes can be used Specific examples that are used in this invention are Direct Black 51, Basic Blue 9, Acid Red 94.

Bromophenol Blue Mordant Black 7.

Reactive Red 6, Disperse Red 17, Solvent Red 214 Fluorescent Blightening Agent 30 and the like.

Suitable examples of surface active agents and conductive resins (hereinafter referred to as -treating agents") are as follows:

A Organic Treating Agents:

(I) Cationic Treating Agents:

(I-a) Amine Type Treating Agents:

Primary, secondary and tertiary alkylamines, cycloalkylamines and alkanolamines, their acid addition salts with carboxylic acids, phosphoric acid or boric acid, and polyalkyleneimines, amideamines and polyamines and their complex metal salts.

(I-b) Imidazoline Type Treating Agents:

I -Hydoxyethyl-2-alkylimidazolines (I-c) Amine-Ethylene Oxide Adducts and Amine-Propylene Oxide Adducts:

Adducts of ethylene oxide, propylene oxide or other alkylene oxide to mono or di-alkanolamines, long-chain (C 12 to C 22) alkylamines or polyamines.

(I-d) Quaternary Ammonium Salts:

Quaternary ammonium salts represented by the following general formula:

F $R J + |R 1 | R 4 l R 3 x wherein R 1 to R 4, which may the same ordifferent, stand for an alkyl group with the proviso that at least 2 of R 1 to R 4 stand for a lower alkyl group and at least one of R 1 to R 4 stands for an alkyl group having at least 6 carbon atoms, preferably at least 8 carbon atoms, and X denotes a halide ion, and quaternary ammonium salts represented by the following general formula:

E R (OCH 2) N-O 1 Xwherein R stands for an alkyl group having at least 12 carbon atoms, p is 0 or I, and X stands for a halide ion.

(le) Other Cationic Treating Agents:

Cationic polymers formed by quaternizing polymers of aminoalcohol I 1,563 208 1.563,208 esters of ethylenically unsaturated carboxylic acids (such as a quaternary ammonium type polymer of diethylaminoethyl methacrylate), acrylamide derivatives (such as a quaternary ammonium type polymer of N,Ndiethylaminoethyl acrylamide), vinyl ether derivatives (such as a pyridium salt of polyvinyl-2-chloroethyl ether), nitrogencontaining vinyl derivatives (such as a product formed by quaternizing poly-2vinylpyridine with p-toluenesulfonic acid), polyamine resins (such as polyethylene glycol polyamine), and polyvinylbenzyltrimethyl ammonium chloride.

( 2) Anionic Treating Agents:

( 2-a) Sulfonic Acid Type Treating Agents:

Alkylsulfonic acids, sulfated oils, and salts of higher alcohol sulfuric acid esters.

( 2-c) Carboxylic Acid Type Treating Agents:

Adipic acid and glutamic acid.

( 2-c) Phosphoric Acid Derivative Treating Agents:

Phosphonic acid, phosphinic acid, phosphite esters and phosphate ester salts.

( 2-d) Other Anionic Treating Agents:

Homopolymers and copolymers of ethylenically unsaturated carboxylic acids (such as polyacrylic acid and copolymers of maleic anhydride with comonomers such as styrene and vinyl acetate), and homopolymers and copolymers of sulfonic acid group-containing vinyl compounds (such as polyvinyltoluenesulfonic acid and polystyrenesulfonic acid).

( 3) Non-Ionic Treating Agents:

( 3-a) Polyether Type Treating Agents:

Polyethylene glycol and polypropylene glycol.

( 3-b) Alkylphenol Adduct Type Treating Agents:

Adducts of ethylene oxide or propylene oxide to alkylphenols.

( 3-c) Alcohol Adduct Type Treating Agents:

Adducts of ethylene oxide or propylene oxide to alcohols (such as a higher alcoholethylene oxide adduct).

( 3-d) Ester Type Treating Agents:

Butyl, amyl and glycerin esters of higher fatty acids such as adipic acid and stearic acid.

( 3-e) Amide Type Treating Agents:

Higher fatty acid amides, dialkyl amides, and adducts of ethylene oxide or propylene oxide to these amides.

( 3-f) Polyhydric Alcohol Type Treating Agents:

Ethylene glycol, propylene glycol, glycerin, pentaerythritol and sorbitol.

( 4) Amphoteric Treating Agents:

Betain type treating agents, imidazoline type treating agents and aminosulfonic acid type treating agents.

B Inorganic Treating Agents:

Alkaline earth metal halides such as magnesium chloride and calcium chloride, inorganic salts such as zinc chloride and sodium chloride, chromium complexes of the Werner type in which trivalent chromium is coordinated with a monobasic acid, and hydrolysis products such as chlorosilane and silicon tetrachloride.

Treating agents exemplified above may be used singly or in the form of a mixture of two or more of them.

A treating agent such as exemplified above is dissolved in a liquid medium substantially incapable of dissolving the inorganic carrier particles to be treated, so that the concentration of the treating agent is maintained at a suitable level, for example, 0 1 to 0 5 % by weight Then, the surface treatment of the carrier particles is performed by dipping the particles into the so formed solution of the treating agent or spraying the solution on the carrier particles.

The particles (A) are dry-blended with the particles (B) at a mixing weight ratio (A):(B) in the range of from 10000:1 to 50:1, preferably from 2000:1 to 100:1 When this mixing ratio (A)/(B) is smaller than 50/1, as illustrated in Comparative Example 2 given hereinafter, the adsorption or adhesion of the fine particles (B) onto the spherical particles (A) becomes insufficient and contamination of the background of the developed copy is often caused to occur.

Further, the fixing property of the resulting developer tends to be degraded If the above mixing ratio (A)/(B) is larger than 10000/1, as is shown in Comparative Example I given hereinafter, the flowability of the developer is reduced and the adaptability of the developer to the developing operation is degraded.

Moreover, the electrical resistance of the developer is increased and there can be only obtained copies having a low contrast and bleeding contours.

The test method and apparatus used for determining the volume resistivity with respect to the particles (A), the particles (B) and dry blends of both the particles (A) and (B) will now be described:

Test Method:

A sample of the particles (A) or the dry blend of the particles (A) and (B) is maintained in a region where a magnetic force (about 680 gauss) acts and it is kept under such conditions that a force other 7 than gravity and magnetic force is not applied to the sample In this state, the sample is contacted with electrodes and the electric resistance is determined according to a customary method The spacing between the electrodes is correctly measured by using a micrometer In this manner the volume resistivity can be determined.

In case of a sample of the fine particles (B), a suitable amount of the sample is placed stationary on the electrode surface.

Other procedures are the same as described above.

The adopted test conditions are as follows:

Electrodes: made up of brass Electrode thickness: 1 mm Magnetic force: about 680 gauss on the surface Electrode spacing: 1 5 mm Applied voltage: 30 to 1,000 V The developer of this invention can be advantageously applied to various electrostatic photographical processes For example, the developer of this invention can be applied to a process disclosed in Japanese Patent Application Laid-Open Specification No 4532/74.

Most preferably, the developer of this invention can be used in the method of developing an electrostatic latent image formed on the surface of an image-bearing material by applying a one component powdery developer thereto which is described and claimed in Specification No.

1,493,280 This method comprises bringing the surface of a developer-retaining member retaining a layer of the powdery developer on its surface into rolling contact with the surface of said image-bearing material at the same surface speed through the developer in such a relation that an accumulation of the developer in excess of that which can pass between the rolling surfaces is formed upstream of the rolling contact zone of both surfaces, and stirring the developer in said accumulation.

The following Examples I-16 illustrate the developer of the invention Four Comparative Examples are also provided.

EXAMPLE I

In 1000 ml of acetone were dissolved and dispersed 35 g of an epoxy resin ("Epiclon" 4050 manufactured by Dai Nippon Ink:

"Epiclon" is a Registered Trade Mark), 60 g of triiron tetroxide (Iron Black B-6 manufactured by Toyo Shikiso) and 5 g of carbon black (Corax-L manufactured by Degussa Co) by means of an attritor The resulting slurry was sprayed in a dry air current maintained at 1300 C by using a two-fluid type injection nozzle and thus dried Then, sieving was conducted to collect spherical particles having a particle size of 2 to 44 It The particles were found to have an oil absorption of 29 8.

The particles were dry-blended with 0 10,, by weight of carbon black (Corax-L particle size 20 to 100 mli) by a V-type mixer to form a developer.

The copying operation was carried out in a copying machine (Model 700 D manufactured by Mita Industrial Co) by using the so prepared developer A clear image having a high contrast and being free of contamination of the background was obtained The flowability of the developer in the developing zone of the copying machine was very good.

The volume resistivity of the developer was 5 9 x 1099-cm (applied voltage of 400 V/cm).

EXAMPLE 2

Spherical particles having a particle size of 2 to 44 p were prepared in the same manner as in Example 1.

The particles were dry-blended with 0 50 by weight of carbon black (Corax-l, particle size 20 to 100 mu) to form a developer The copying operation was carried out in a copying machine (Model 700 D) by using the so prepared developer.

An image having a high contrast but being free of contamination of the background was obtained The flowability of the ,developer in the developing zone of the copying machine was very good.

The volume resistivity of the developer was 8 5 x 108 Q 2-cm (applied voltage of 400 V/cm).

COMPARATIVE EXAMPLE I Spherical particles having a particle size of 2 to 44 p were prepared in the same manner as in Example 1.

The particles were dry-blended with 0.005 ' by weight of carbon black (Corax-L, particle size 20-100 m A) to form a developer The copying operation was carried out in a copying machine (Model 700 D) by using the so prepared developer.

An image having a low contrast in which an edge effect and bleeding of contours were observed was obtained It was found that the flowability of the developer in the developing zone was very bad The volume resistivity of the developer was 3 3 x 1014 Q_ cm (applied voltage of 400 V/cm).

COMPARATIVE EXAMPLE 2 Spherical particles having a particle size of 2 to 44 p were prepared in the same manner as in Example 1.

The particles were dry-blended with 50,, by weight of carbon black (Corax-L, particle size 20-100 mp) to form a developer The copying operation was 8 1.563,208 1,563,208 carried out in a copying machine (Model 700 D) by using the so prepared developer.

The background of the resulting image was extremely contaminated with excessive carbon black which did not adhere to the spherical particles but were present in the floating state.

The volume resistivity of the developer could not be measured according to the above-mentioned method and apparatus because of the leaking phenomenon.

COMPARATIVE EXAMPLE 3 A mixture of 100 g of an epoxy resin, 600 g of triiron teroxide, 3 g of an azine type dye and 2 g of carbon black was dispersed in 5,000 ml of acetone, and by conducting the spray-drying and sieving in the same manner as in Example I particles having a size of 2 to 44,u were prepared The particles were not spherical but amorphous The copying operation was carried out in a copying machine ( 700 D) by using the particles as a developer In the resulting copied image.

contamination of the background was conspicuous and contours were bleeding.

The flowability of the developer in the developing zone of the copying machine was very bad The volume resistivity of the developer was 1 3 x 10105-cm (applied voltage of 400 V/cm).

COMPARATIVE EXAMPLE 4 A mixture of 4 parts by weight of an epoxy resin and 6 parts by weight of triiron tetroxide was sufficiently kneaded and milled by two hot rolls The kneaded mixture was pulverized and sieved to obtain particles having a particle size of 2 to 44,u.

These particles had a pseudo-cubic form including sharp sides These particles were made spherical in a hot air current maintained at 530 WC to obtain particles having lustrous particles The oil absorption of the particles was 17 6.

The so prepared particles were dryblended with 0 5 %, by weight of carbon black (Corax-L) to form a developer.

The copying operation was carried out in a copying machine (Model 700 D) by using the so prepared developer The background of the obtained image was extremely contaminated with carbon black which did not adhere sufficiently to the particles.

The volume resistivity of the developer was 1 O x 109 Q-cm (applied voltage of 400 V/cm).

Properties of developers obtained in the foregoing Examples 1 and 2 and Comparative Examples I to 4 and images obtained by using these developers were examined and evaluated in the following manners Obtained results are shown in Table 1.

Bleeding By the term -bleeding" is meant a phenomenon in which sharp portions of figures or patterns are seen thick or peripheral portions are obscure The bleeding was evaluated according to the following scale:

O:no bleeding A:slight bleeding x: conspicuous bleeding Fog By the term -fog" is meant a phenomenon in which the background is contaminated with specks or dots The fog is evaluated according to the following scale:

0: no fog a: slight fog x: extreme fog Edge Effect By the term "edge effect" is meant a phenomenon in which central portions of, for example, figures are not printed sufficiently but left blank, whereas peripheral portions are printed densely The edge effect is evaluated according to the following scale:

0: no edge effect A: peripheral portions printed more heavily than central portions x: central portions of, for example, figures left completely unprinted (blank).

Image Density By the term "image density" is meant a reflection density of the image The image density is evaluated according to the following scale:

0: reflection density higher than 1 5 A: reflection density of 1 to 1 5 x: reflection density lower than 1 Fixing Property By the term "fixing property" is meant the adhesion strength of the developer to the copy The fixing property is evaluated according to the following scale:

0: the developer was not rubbed off the copy by strong rubbing with a finger A: when the image is rubbed with a finger, some developer is rubbed off the copy, and the copy background is contaminated x: when the image is rubbed with a finger.

the developer is easily rubbed off the copy.

Flowability The flowability is evaluated based on the flow of the developer on a developing roller according to the following scale:

0: the developer flows smoothly without agglomeration A: small agglomerates are formed and the flowing is less smooth than for O x: a number of large agglomerates are formed and the developer does not flow smoothly 1,563,208 10 Scattering The scattering tendency of the developer is evaluated according to the following scale:

O O: no scattering of the developer and no Volume ReShape of sistivity Sample Particles ( 52-cm) Bleeding Example I spherical 5 9 x 1109 Example 2 ditto 8 5 x 108 O Comparative Example I ditto 3 3 x1104 A Comparative Example 2 ditto leaking O Comparative Example 3 amorphous 1 3 x 10 ' X Comparative Example 4 spherical L O x 109 O Examples A to D below illustrate the production of the particles (A).

EXAMPLE A

A dispersion of 50 g of an epoxy resin ("Epikote" 1004 manufactured by Shell Chemical, "Epikote" is a Registered Trade Mark) and 50 g of triiron tetroxide in 1 I of acetone was sprayed in a dry air current maintained at 130 C and thus dried The resulting particles were sieved to collect particles having a size of 2 to 44 u The volume resistivity of the so prepared particles was higher than Ix 104 Q-cm.

EXAMPLE B

In I I of a 1:1 mixed solvent of acetone and toluene were dissolved and dispersed 35 g of an epoxy resin ("Epokite" 1004), 60 g of triiron tetroxide and 5 g of carbon black, and the dispersion was spray-dried in a dry air current maintained at 130 C The resulting particles were sieved to collect particles having a size of 2 to 44 u The volume resistivity of the particles was 3.7 x 10 '32-cm.

EXAMPLE C

In I I of hot toluene were dissolved and dispersed 27 g of a petroleum resin which is an alicyclic hydrocarbon resin with repeating units of formula wherein the number average molecular weight is about 1200 ("Hi-rez" P-10 OLM contamination of the developing zone or the background with the developer

A: slight scattering x: conspicuous scattering Printed Image Developer Edge Den Fixing Flowa ScatterEdge f ProperFog Effect sity ty bility ing O O O O O O O O O A O O o A A O L O x O O A A A x O A X X A x O A O O manufactured by Mitsui Sekiyu K K, 'Hirez" is a Registered Trade Mark), 38 g of polypropylene (Biscol 550-P manufactured by Sanyo Kasei K K) and 35 g of triiron tetroxide, and the dispersion was spraydried in a dry air current maintained at C The resulting particles were sieved to collect particles having a size of 2 to 44/u.

The volume resistivity of the particles was higher than Ix 1014 g-cm.

EXAMPLE D

In I I of hot toluene were dissolved and dispersed 26 g of a saturated alicyclic resin which is a hydrogenated styrene resin with repeating units of formula CH 2 CH /\ CH CH 2 CH 2 CH 2 CH 2 C 2 wherein the molecular weight is about 770 ("Arkon" P-115 manufactured by Arakawa Rinsan Kagaku K K, "Arkon" is a Registered Trade Mark), 11 g of an ethylene-vinyl acetate copolymer (Evaflex 420 manufactured by Mitsui Polychemical K K), 55 g of triiron tetroxide and 8 g of carbon black, and the dispersion was spray-dried in a dry air current maintained at 150 C The resulting particles were sieved to collect particles having a size of 2 to 44 / The volume resistivity of the particles was 2 1 x 10 '3 Q-cm.

Examples E to R illustrate the production of particles (B).

1,563,208 1.563208 II EXAMIPLE E In 20 ml of water xas completely dissolved O 3 g of Direct Black 51 (C I.

27720), and 10 g of finely divided silica ("Aerosil" A 200 manufactured by Nippon Aerosil K K) was added to the dye solution and sufficiently dispersed in the solution by a ultrasonic vibrator to thereby make the dye uniformly adsorbed on the surface of the finel R divided silica The solvent was evaporated and the residue was dried Then, the dye-adsorbed silica was treated in a ball mill to reduce the particle size to 30-100 m/t The volume resistivity of the so obtained particles was 3 O x 1107 Q-cm.

EXAMPLE F

In 10 ml of water was completely dissolved I ml of an ampholytic surfactant of the dimethyl alkylbetaine type of formula CH 3 R N+ CH 2 COOCH, (Anon BF manufactured by Nippon Oils and Fats Co Ltd) and 10 of finely divided silica was added to the activator solution and sufficiently dispersed therein The solvent was evaporated and the residue was dried to thereby obtain silica particles having the activator uniformly adsorbed thereon and a particle size of 30-100 msa.

The volume resistivity of the so treated silica particles was 2 7 x 101 Q-cm.

EXAMPLE G

In 20 ml of an aqueous solution of sodium hydroxide was completely dissolved 0 5 g of Sulfur Black 2 (C 1 53195), and 10 g of activated clay having a size smaller than 5 m was sufficiently dispersed in the dye solution to thereby make the dye uniformly adsorbed on the surface of the activated clay The solvent was evaporated, and the residue was dried and pulverized to obtain fine particles having a volume resistivity of 4 5 x 109 Q-cm and a particle size of 30-5000 my.

EXAMPLE H

To a solution of 0 5 g of Acid Red 94 (C 1.

45440) in 20 ml of methanol was added 10 g of finely divided silica ("Aerosil" A 200), and the finely divided silica was sufficiently dispersed in the dye solution to make the dye uniformly adsorbed on the surface of the finely divided silica The dye-adsorbed silica was dried to obtain fine particles having a volume resistivity of 8 9 x 11092-cm and a particle size of 30 to 100 mp.

EXAMPLE I

In 100 ml of methanol was dissolved 100 g of the conductive resin poly( 2methacrvloxyethvltrimethyl ammonium chloride) with repeating units of formula CH CH 2-C 0 = -O-CH 2 CH 2-N (CH 3) 3 C 1n (BR 013 manufactured by Toyo Ink K K solid content= 45 ,, by weight), and 100 g of finely divided silica ("Aerosil" A 200) was incorporated and dispersed in the solution.

The resin-adsorbed silica was dried to obtain fine particles having a volume resistivity of 2 3 x 1083 Q-cm and a particle size of 30-100 mol.

EXAMPLE J

In a solution of 0 5 g of Bromophenol Blue in 20 ml of an aqueous solution of sodium hydroxide was incorporated and dispersed 10 g of finely divided silica ("Aerosil" A 200) to make the dye sufficiently and uniformly adsorbed on the silica The dye-adsorbed silica was dried to obtain fine particles having a volume resistivity of 7 4 x 107 Q-cm and a particle size of 30-100 mu.

EXAMPLE K

Carbon black ( 50 g) (Mitsubishi Carbon Black 130 manufactured by Mitsubishi Kasei K K) was treated in a ball mill having a capacity of I liter to disentangle agglomerates The volume resistivity of the so treated fine particles of carbon black (particle size 20-100 mru) could not be measured because of the leaking phenomenon.

EXAMPLE L

Carbon black ( 50 g) (Corax-L) was treated in a ball mill having a capacity of 1 liter to disentangle agglomerates The volume resistivity of the fine particles of carbon black (particle size 20-100 mu) could not be measured because of the leaking phenomenon.

EXAMPLE M

In an aqueous solution containing a surface active agent, 10 g of finely divided silica having a size not exceeding 100 my was washed under ultrasonic vibrations to effect degreasing, and then, the silica particles were sufficiently washed with water, and they were subjected to nonelectrolytic plating in the following manner.

The silica particles were immersed in a solution of 10 ml of a pre-treating liquid for non-electrolytic plating (Sensitizer manufactured by Nippon Kanizen K K) in ml of water for about 5 minutes to activate the silica particles Then, the activated silica were recovered by filtration.

1,563,208 1 1 1 1 1,563,208 Then, the particles were treated in a solution of 20 ml of a pre-treating liquid for non-electrolytic plating (Activator manufactured by Nippon Kanizen K K) in 80 ml of water for 3 to 5 minutes to effect the activating treatment Then, the activated particles were recovered by filtration, and they were dipped in a solution of 40 ml of a non-electrolytic nickel-plating liquid (Blue-Sumer manufactured by Nippon Kanizen K K) in 160 ml of water for 5 to 10 minutes to deposit metallic nickel on the surfaces of the silica particles The plated particles were collected by filtration, washed with water and dried The volume resisitivity of the so plated fine silica particles was 5 3 x 1049-cm and their particle size was 30-120 miu.

EXAMPLE N

In the same manner as described in Example M, 10 g of fine particles of activated clay having a particle size smaller than 100 mg were pre-treated Then, they were dipped in a chemical copper-plating liquid (manufactured by Okuno Seiyaku Kogyo K K) for 5 to 10 minutes under agitation to deposit non-electrolytically copper on the surfaces of the activated silica particles The volume resistivity of the resulting copper-plated particles was 6.5 x 104 Q-cm and their particle size was 30mru.

EXAMPLE O

In the same manner as described in Example M, 20 g of finely divided triiron tetroxide having a particle size smaller than I,A was pre-treated Then, the pre-treated triiron tetroxide was dipped in a chemical silver-plating liquid ldisclosed on page 1234 of the Handbook of Chemistry ( 1973 edition) compiled by Japanese Chemical Societyl for 2 to 5 minutes under agitation to deposit non-electrolytically silver on the surface of the finely divided triiron tetroxide The volume resistivity of the so plated triiron tetroxide was 2 3 x 1040-cm and the size of the resulting particles was 2001020 mu.

EXAMPLE P

Reduced copper powder (manufactured by Fukida Kinzoku Hakufun K K) was classified by a sieve to collect fine particles of copper having a size of 4 g' or less The volume resistivity of the copper powder (particle size 0 1-4 M) could not be measured because of the leaking phenomenon.

EXAMPLE Q

Silver powder was classified by a sieve to collect fine particles having a size of 4, or less The volume resistivity of the silver powder (particle size O 1-4) could not be measured because of the leaking phenomenon.

EXAMPLE R

Iron powder (manufactured by Nippon Teppun K K) was classified by a sieve to collect fine particles having a size of 4, or less The volume resistivity of the iron powder (particle size 0 1-4 Ii could not be measured because of the leaking phenomenon.

Examples 3 to 16 below illustrate developers prepared by dry-blending particles (A) prepared in Examples A to D with particles (B) prepared in Example E to R at the (A):(B) mixing weight ratios in the range of from 10000:1 to 50:1.

EXAMPLE 3

A developer was prepared by dryblending 100 parts by weight of the particles obtained in Example A sufficiently with 0 1 part by weight of the fine particles obtained in Example E by using a V-type mixer The copying operation was carried out on white copying paper in a copying machine of the heated roll fixing type (Model 700 D manufactured by Mita Industrial Co) by using this developer A clear copied image of a sheer black color was formed The developer prepared in this Example had a better flowability than that of the particles obtained in Example A, and the volume resistivity of the developer was reduced to 8.3 x 10162-cm though the volume resistivity of the particles obtained in Example A was higher than 1014 Q-cm.

EXAMPLE 4

In a mill filled with glass beads, 100 parts by weight of the particles obtained in Example B were dry-blended sufficiently with 0 1 part by weight of the fine particles obtained in Example F to form a developer.

The copying operation was carried out in a copying machine (Model 700 D) by using the so prepared developer A clear copied image of a sheer black color being free of contamination in the background was obtained The flowability of the developer was better than the flowability of the particles obtained in Example B, and the volume resistivity of the developer was as low as 5 0 x 10 ' 1 Q-cm, though the volume resistivity of the particles obtained in Example B 3 7 x 10 '3 Q-cm.

EXAMPLE 5

In a sand mill, 100 parts by weight of the particles obtained in Example C were dryblended sufficiently with 0 05 part by weight of the fine particles obtained in Example G to form a developer The copying operation was carried out in a copying machine of the 1,563,208 pressure fixing type (Mita -Copystar" 350 D manufactured by Mita Industrial Co, -Copystar" is a Registered Trade Mark) by using the so prepared developer A copy having an image of a sheer black color free of contamination in the background was obtained The developer had a good flowability and the volume resistivity of the developer was as low as 3 1 x 10101-cm, though the volume resistivity of the particles obtained in Example C was higher than 62-cm.

EXAMPLE 6

By means of a V-type mixer 100 parts by weight of the particles obtained in Example D were dry-blended sufficiently with 0 04 part by weight of the fine particles obtained in Example H to form a developer The copying operation was carried out in a copying machine (Mita "Copystar" 350 D) by using the so prepared developer A print having an excellent constant and being free of fog was obtained The developer was excellent in the flowability and agglomeration was not observed at all The volume resistivity of the developer was as low as 4 O x 10102-cm, though the volume resistivity of the particles obtained in Example D was 2 1 x 101352-cm.

EXAMPLE 7

In a sand mill, 100 parts by weight of the particles obtained in Example A were dryblended sufficiently with 0 05 part by weight of the fine particles obtained in Example J to obtain a developer The copying operation was carried out on white copying paper in a copying machine (Model 700 D) by using the so prepared developer A clear black image having high density and contrast and free of fog was obtained The volume resistivity of the developer was 7.3 x l 09 Q-cm.

EXAMPLE 8

By means of a V-type mixer, 100 parts by weight of the particles obtained in Example B were dry-blended sufficiently with 0 02 part by weight of the fine particles obtained in Example L to form a developer The copying operation was carried on white copying paper in a copying machine (Model 700 D) by using the so prepared developer. A clear copied image having a high contrast

and free of fog was obtained No agglomeration was observed in the developer, and the volume resistivity of the developer was as low as 7 3 x 108 Q-cm.

EXAMPLE 9

By means of a V-type mixer, 100 parts by weight of the particles obtained in Example C were dry-blended sufficiently with 0 3 part by weight of the fine particles obtained in Example I to form a developer The copying operation was carried out on white copying paper in a copying machine (Mita Copystar" 350 D) by using the so prepared developer A black image having a high contrast and free of fog was obtained The volume resistivity of the developer was as low as 6 5 x 11099-cm.

EXAMPLE 10

By means of a V-type mixer, 100 parts by weight of the particles obtained in Example D were dry-blended with 0 1 part of the fine particles obtained in Example K to form a developer The copying operation was carried out in a copying machine (Mita "Copystar" 350 D) by using the so prepared developer A clear print free of contamination in the background was obtained The developer had a very good flowability and the volume resistivity of the developer was 4 4 xl 09 Q-cm.

EXAMPLE 11

By means of a V-type mixer, 100 parts by weight of the particles obtained in Example A were dry-blended with 0 3 part by weight of the fine particles obtained in Example M to form a developer The copying operation was carried out in a copying machine (Model 700 D) by using the so prepared developer A clear print was obtained The volume resistivity of the developer was 6.9 x 101 9-cm.

EXAMPLE 12

A developer was prepared by dry 95 blending 100 parts by weight of the particles obtained in Example B with 0 05 part by weight of the fine particles obtained in Example N The copying operation was carried out in a copying machine (Model 100 700 D) by using the so prepared developer.

A print free of bleeding but having a high density was obtained The developer had a good flowability, and the volume resistivity of the developer was 1 4 x 109 Q-cm 105 EXAMPLE 13

A developer was prepared by dryblending 100 parts by weight of the particles obtained in Example C with I part by weight of the fine particles obtained in Example 0 110 to form a developer The copying operation was carried out in a copying machine (Mita "Copystar" 350 D) by using the so prepared developer A print having a high density and an excellent fixing property was obtained 115 The volume resistivity of the developer was 9.Ox 100 2-cm.

EXAMPLE 14

A developer was prepared by dryblending 100 parts by weight of the particles 120 obtained in Example D with 1 0 part by 1,563 208 weight of the fine particles obtained in Example P to form a developer The copving operation was carried out in a copying machine (Mita "Copystar" 350 D) by using the so prepared developer A print being free of contamination in the background and having a high density and an excellent fixing property was obtained.

The volume resistivity of the developer was 7 7 x 1090 Q-cm.

EXAMPLE 15

A developer was prepared by dryblending 100 parts by weight of the particles obtained in Example A with 1 5 parts by weight of the fine particles obtained in Example Q to form a developer The copying operation was carried out in a copying machine (Model 700 D) by using the so prepared developer A clear print having a high density was obtained The developer had a good flowability and the volume resistivity of the developer was 5 1 xl O 99cm.

EXAMPLE 16

A developer was prepared by dryblending 100 parts by weight of the particles obtained in Example C with 20 parts by weight of the fine particles obtained in Example R to form a developer The copying operation was carried out in a copying machine (Mita "Copystar" 350 D) by using the so prepared developer A clear print free of bleeding was obtained The volume resistivity of the developer was 4 6 x 10 '0 PQ-cm.

Claims

WHAT WE CLAIM IS:-

1 A flowable developer having a volume resistivity not higher than 10129-cm, suitable for use in electrostatic photography, said developer consisting essentially of a dry blend of (A) substantially spherical magnetic particles comprising a binder medium with from 20 % to 80/,', by weight, based on the weight of particles (A), of particles of a magnetic material distributed therein, said particles (A) having a rough surface formed by spray-drying a dispersion of said magnetic particles distributed in a solution of said binder medium in an organic solvent and having an average particle size of from I to 100 microns, and (B) particles of a material having a volume resistivity not higher than 10 '

2 Q-cm, said particles (B) having an average particle size not larger than 1/10 of the average particle size of the particles (A) and being distributed predominantly on the surface of the particles (A), the particles (A) and (B) being present in a weight ratio of (A):(B) of from 10000:1 to 50:1 60 2 A developer according to claim I wherein the binder medium is a resin rubber or wax capable of exhibiting adhesiveness under application of heat or pressure.

3 A developer according to claim 2 65 wherein the particles (A) comprise 40 to ',, by weight of a fine pownder of a magnetic material 30 to 59 %,, by weight of a resin, rubber or wax binder medium and I to ", by weight of carbon black 70

4 A developer according to claim 2 or 3 wherein the resin is an epoxy resin.

A developer according to any one of the preceding claims wherein the magnetic material is a fine powder of triiron tetroxide 75 having a particle size smaller than 500 mp.

6 A developer according to any one of the preceding claims wherein the particles (A) have an average particle size of from 2 to 50 microns 80

7 A developer according to any one of the preceding claims, wherein the particle size distribution of particles (A) is such that from 0 to 10 ",, of said particles are larger than 44,u and from 0 to 10 , of said particles 85 are smaller than 2,u.

8 A developer according to any one of the preceding claims wherein the particles (A) have an oil absorption of from 25 to 40.

9 A developer according to any one of 90 the preceding claims wherein the particles (B) are carbon black.

A developer according to any one of the preceding claims wherein the particles (A) and the fine particles (B) are present in a 95 weight ratio (A):(B) in the range of from 2000:1 to 100:1.

11 A developer according to any one of the preceding claims wherein the particles (A) are formed by dissolving the binder 100 medium in an organic solvent so that the binder medium concentration in said solvent is not higher than 30 ', by weight, dispersing a fine powder of a magnetic material in the resulting solution, spray 105 drying the resulting slurry and, if appropriate, sieving the resulting particles.

12 A developer according to claim I wherein particles (A) are substantially as hereinbefore described in any one of 110 Examples A to D.

13 A developer according to claim I wherein particles (B) are substantially as hereinbefore described in any one of' Examples E to R 115 14 A developer according to claim 1, substantially as hereinbefore described in any one of Examples I or 3 to 16.

A developer according to claim 1.

1,563,208 substantially as hereinbefore described in Example 2.

16 A copy sheet bearing an image which has been developed from an electrostatic latent image using a developer as claimed in any one of claims I to 15.

J A KEMP & CO, Chartered Patent Agents.

14 South Square, Grav's Inn.

London WC 1 R 5 EU.

Printed for Her Majestxs Stationery Office b, the Courier Press Leamington Spa, 1980 Published by The Patent Office 25 Southampton Buildings London WC 2 A l AY, from which copies may be obtained.